Quake reminder of Puente Hills fault

7.5 Temblor on Puente Hills fault would be disastrous

March 31, 2014

A bigger earthquake along the lesser-known fault that gave Southern California a moderate shake Friday could do more damage to the region than the long-dreaded ‘Big One’ from the more famous San Andreas Fault, experts warn.

The Puente Hills thrust fault, which brought Friday night’s magnitude 5.1 quake centered in La Habra and well over 100 aftershocks by Sunday, stretches from northern orange County under downtown Los Angeles into Hollywood- a heavily populated swath of the Los Angeles area.

Potential earthquakes on the Puente Hills fault beneath the Los Angeles area could result in 3,000 to 18,000 fatalities, 142,000 to 735,000 displaced households, and more than $250 billion in total damages, according to U.S. Geological Survey (USGS and Southern California Earthquake Center (SCEC) research.

The researchers determined a probable range of estimated losses by averaging losses predicted under each scenario and model. The scenarios all assumed an earthquake occurring at 2 p.m. during a weekday, when many people are at work. The number of casualties would be significantly less if an earthquake were to occur on the fault at night when most people are at home.

In contrast, a larger magnitude 8 quake along the San Andreas would cause an estimated 1,800 deaths.

Lucy Jones, a U.S. Geological Survey geologist, said an earthquake along the fault could be particularly hazardous because it is a horizontal fault, which means more intense shaking could be felt over a larger area than vertical faults like the Newport-Inglewood or Hollywood.

Shaking from an earthquake in the heart of Los Angeles, where there are older, more vulnerable building, could be so intense that heavy objects would be lifted into the air.

“That’s the type of shaking that will hit all of downtown. And everywhere from la Habra to Hollywood,” Jones said.

“In terms of location, it couldn’t be much worse,” said James Dolan, a professor at University of Southern California’s department of Earth sciences, told National Geographic in 2003 while working on a study of faults. “Downtown L.A. is sitting on top of this thing.”

Scientists believe a major quake happens along the fault roughly every 2,500 years, but don’t know when the last one was, the L.A. Times reports.

In 1987, the fault caused the Whittier narrows earthquake. Still considered moderate at magnitude 5.9, that quake killed eight people and did more than $350 million in damages.